1. Field of the Invention
The present invention relates to the construction of a vehicle track. More specifically, the present invention concerns the construction of the lugs or ribs on an endless track for tracked vehicles such as snowmobiles.
2. Description of Related Art
The basic platform for a conventional snowmobile includes a chassis that has at least three basic components: (1) a tunnel at the rear of snowmobile, (2) an engine cradle connected at the front of the tunnel, and (3) a front suspension connected beneath the engine cradle. The three components are connected together to form a unitary structure that is rigid enough to withstand the forces impingent thereupon during operation of the snowmobile.
In the conventional snowmobile, the tunnel is an inverted, U-shaped structural member that is disposed above an endless track, which propels the vehicle by engaging the ground or snow beneath the vehicle. The engine cradle is the structural portion of the chassis that extends forwardly from the tunnel and supports the engine at the front of the vehicle. The front suspension is a part of the engine cradle located beside and beneath the engine cradle. Steering skis (usually two) are suspended from the front suspension and engage the terrain beneath the vehicle. Shock absorbers, operatively disposed between the skis and the chassis, dampen the forces encountered by the skis as the vehicle travels over either groomed or rough terrain. The endless track is usually suspended beneath the tunnel via a structure called the “rear suspension.” The rear suspension connects to the tunnel via one or more shock absorbers to dampen the forces that impinge upon the endless track as the vehicle travels over the ground.
Snow groomers are tracked vehicles typically used to groom the snow on ski slopes at winter resort areas. The platform for conventional snow groomers usually includes a number of elements such as: (1) a frame, (2) two endless tracks disposed on either lateral side of the frame, (3) an engine mounted on the frame, operatively connected to the two endless tracks, and (4) a cabin mounted on the frame to house one or more persons therein.
The endless tracks of the snow groomer typically are threaded around several wheels suspended on either lateral side of the frame. Typically, the endless tracks are hydraulically connected to the engine such that the endless tracks may be controlled independently. When equal amounts of motive power are applied to both tracks simultaneously, the snow groomer moves in a straight line. When differing amounts of motive power are applied to the two endless tracks a the same time, one track overpowers the other to steer the snow groomer (in the same manner that a military tank is steered).
Whether discussing a snowmobile, a snow groomer, or any other type of vehicle that relies on an endless track for propulsion, tracked vehicles drivingly engage the ground through the one or more endless tracks provided thereon. Endless tracks conventionally include an inner side that is engagable with the propulsion system of the vehicle. Conventional tracks also include an outer side with a pattern of projecting lugs or ribs that are designed to engage the snow or other ground surface, apply traction, and propel (or brake) the vehicle.
The prior art is replete with examples of endless tracks. In fact, a number of patents address some of the different ways in which the traction characteristics of endless tracks may be improved. U.S. Pat. Nos. 4,991,911, 5,722,745, and 6,109,705 provide three such examples.
Regardless of the vehicles on which endless tracks are provided, endless tracks must provide two types of traction: propulsive traction and braking traction. Propulsive traction pushes the vehicle forward while braking traction slows or stops the vehicle. In some cases, the track may be operated in a direction opposite to that required for propulsion. If so, the braking traction is characterized as a reverse propulsive traction. During propulsion, a forward face of the lugs engages the ground or the snow. Conversely, during braking, a rearward face of the lugs engages the ground or snow.
A common example of a conventional snowmobile track includes a plurality of lugs that are rectangularly-shaped (whether viewed from a top plan view or front or rear elevational view). When configured in this manner, the lugs provide the same traction whether they engage the ground or snow in a propulsive or in a braking fashion. Moreover, in the simple, traditional example, the lugs are disposed laterally across the endless track. So disposed, the lugs are positioned perpendicularly to the travel direction of the endless track.
Other snowmobile tracks are also known in the prior art. For example, U.S. Pat. No. 5,713,645 discloses an endless track with a plurality of V-shaped lugs with the points of the lugs directed rearwardly (or opposite to the forward travel direction of the endless track). The lugs provide propulsive traction because the open part of the V-shape (the forward face) forms a cup that grabs snow when the endless track pushes the snowmobile forward. While this improves the propulsive traction of the endless track, braking traction is sacrificed. When the vehicle brakes (or is operated in reverse), the rearward, pointed face of the V-shape diminishes traction because it does not present a cup-shaped surface to “scoop” at the ground or snow.
As would be appreciated by those skilled in the art, the V-shaped lug provides more traction when operating in a propulsive fashion than a laterally-oriented, flat lug. Conversely, the V-shaped lug provides less traction when operated in a braking fashion (or in reverse) than the simple, laterally-oriented, rectangular lug.
As would be appreciated by those skilled in the art, the same characteristics that help a vehicle track gain traction by digging into the snow inhibit the track's ability to turn. This is because the longitudinal portion of the track that is in contact with the snow is typically very long (e.g., 1 to 2 meters). The lugs are disposed in a pattern over the length of the track. Since the lugs are largely inflexible in the lateral direction, the vehicle's operator must exert a significant steering force to push the lugs sideways through the snow to turn the track.
Because a conventional endless track for a snowmobile inhibits turning, a need has arisen for an endless track that does not do so. The prior art to date, however, has failed to provide such a track.